F36 Change: Relocate RPM database to /usr (System-Wide Change proposal)

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/RelocateRPMToUsr

== Summary ==
Currently, the RPM databases is located in `/var`. Let's move it to
`/usr`. The move is already under way in rpm-ostree-based
installations, and in (open)SUSE.

== Owner ==
* Name: [[User:chrismurphy| Chris Murphy]], [[User:Salimma|Michel
Alexandre Salim]], [[User:Ngompa|Neal Gompa]]
* Email: bugzilla(a)colorremedies.com, michel(a)michel-slm.name, ngompa13(a)gmail.com


== Detailed Description ==
=== Current location ===
<pre>/var/lib/rpm</pre>

=== New location ===
<pre>/usr/lib/sysimage/rpm</pre>

<code>/var/lib/rpm</code> will be a symlink pointing to
<code>/usr/lib/sysimage/rpm</code>

Changing the file system layout to accommodate a snapshot+rollback
regime is implied, but not required by this proposal. For example,
Fedora has long placed `/home` on a separate subvolume (or file
system) so it can be isolated from system root. Likewise, it makes
sense to isolate `/var/log` and possibly `/var/lib/libvirt/images` so
these locations continue to carry forward in time, even if the system
root does a rollback.

== Feedback ==

There will be no change to DNF as part of this change proposal. DNF's
history will remain in `/var` until DNF 5. Discussion continues about
the effect of a snapshot+rollback regime on DNF history.
[http://lists.rpm.org/pipermail/rpm-ecosystem/2021-December/000769.html
Relocate DNF history to /usr.]

Upstream RPM accept the change, but institutionally don't like the
loss or weakening of a
[http://lists.rpm.org/pipermail/rpm-ecosystem/2021-December/000781.html
very well known location] for the database, and
[http://lists.rpm.org/pipermail/rpm-ecosystem/2021-December/000781.html
anticipate complaints].


== Benefit to Fedora ==

* The RPM database primarily describes the state of `/usr`. Storing
the databases in `/usr` will more easily facilitate OS rollback,
without affecting `/var`.

* Helps align Fedora variants with each other
** rpm-ostree based systems (including CoreOS, IoT, Silverblue,
Kinoite) already use `/usr/lib/sysimage` for rpmdb.

* Consistency with another RPM-based distro, (open)SUSE has made this change

* Accounts for various snapshot+rollback regimes, i.e. it's a
beneficial change whether Btrfs or device-mapper based regimes.


== Scope ==
* Proposal owners:
** changes in rpm package
*** create the new path
*** create a symlink for the old path pointing to new path

* Other developers:
** changes in SElinux policy

* Release engineering: [https://pagure.io/releng/issue/10441 #Releng
issue 10441]
* Policies and guidelines: N/A (not needed for this Change)
* Trademark approval: N/A (not needed for this Change)
* Alignment with Objectives:

== Upgrade/compatibility impact ==
Change will be applied to offline upgrades, similar to the RPM sqlite
database change. A systemd service will move the rpmdb from /var to
/usr, then create a symlink pointing to /usr from /var.

# Create `/usr/lib/sysimage/rpm` (rpm package will do this at preinst)
# Create symlinks in `/usr/lib/sysimage/rpm/` pointing to files in
`/var/lib/rpm/` (rpm package will do this at preinst)
# Change the dbpath in `/usr/lib/rpm/macros` to
`/usr/lib/sysimage/rpm` (rpm package will be patched to do this on
F36+)
# Request rpm rebuild the database (done via systemd service)
# Remove `/var/lib/rpm` and create a symlink `/var/lib/rpm` ->
`/usr/lib/sysimage/rpm` (done via systemd service)


== How To Test ==

# Perform a new clean install, or upgrade a system
# Check that `/var/lib/rpm` is a symlink to `/usr/lib/sysimage/rpm`
# Check that `/usr/lib/sysimage/rpm` is populated with at least
`rpmdb.sqlite`, possibly also `rpmdb.sqlite-shm` and
`rpmdb.sqlite-wal`
# Confirm `rpm -q <package>` and/or `rpm -qa` still work

== User Experience ==

* symlink `/var/lib/rpm` -> `/usr/lib/sysimage/rpm`

Otherwise, the change should be invisible to users.

== Dependencies ==
* `rpm-ostree` probably should make `/usr/share/rpm` a symlink to
`/usr/lib/sysimage/rpm`, rather than the reverse as it is currently.
* `PackageKit` might use inotify on `/var/lib/rpm` need to check if it
does and whether it should be changed or add the additional path


== Contingency Plan ==
* Contingency mechanism: Revert the change, try again the next Fedora release.
* Contingency deadline: Beta freeze
* Blocks release? Yes

-- 
Ben Cotton
He / Him / His
Fedora Program Manager
Red Hat
TZ=America/Indiana/Indianapolis